A switch circuit that supplies current with an inductive load such as a motor connected to a DC power supply, a choke coil or a transformer is widely used in computers, automobiles, home electrical appliances, and industrial instruments.
A flywheel circuit is known as an art for recovering magnetic energy of a switch circuit that supplies current to an inductive load. FIG. 1 is a diagram of a flywheel circuit. Referring to FIG. 1, a main switch SW1, an inductive load L01, and a resistance R01 such as an equivalent serial resistance of the inductive load are connected in series with a DC power supply. A diode D01 is connected in parallel with the inductive load L01. In the flywheel circuit, current Ion flows during a period when the main switch SW1 is ON. During a period when the main switch SW1 is OFF, current Ioff resulting from magnetic energy stored in the inductive load L01 flows through the diode D01. It is thus possible to recover the magnetic energy stored in the inductive load L01.
Further, in Patent Documents 1 through 3, there are disclosed, as methods for recovering magnetic energy when the current that flows in the inductive load is cut off, a method that utilizes resonance of coil and capacitor, or a method for forming four switch circuits in a bridge.    Patent Document 1: Japanese Patent No. 2616713    Patent Document 2: Japanese Patent No. 3634982    Patent Document 3: Japanese Patent No. 3735673